1. Field of the Invention
An embodiment, including related aspects, of the present invention relates to a method for the partial or total modification of functional groups on the surface of polymeric or polymer-containing materials, by means of combined plasma functionalization and localized thermal defunctionalization. In an aspect at first, a surface of a material is exposed to cold plasma, whereby a desired polymer functionalization is achieved. After the plasma-treatment, the surface is locally heated in an optional manner, primarily by means of an electron beam, resulting in the local defunctionalization of the heated area. By directing the electron beam across the surface of the material, any desired distribution of functional groups can be obtained on the surface. Another embodiment, including related aspects, of the present invention relates to a device enabling the performance of such a treatment.
2. Presentation of the Problem
Polymeric or polymer-containing materials (in the following text: polymer material) exhibit surface properties determined by the polymer type. It is oftentimes desirable to modify the surface properties of a polymer material. The modification of surface properties is desirable, especially owing to the need for biocompatibility of the materials (with various implants, prostheses, and for the culture of biological cells and fibrils), or the need to improve the adhesion of various coating materials on a polymer surface. Normally, the surface of a polymer material has to be activated to enhance its wettability and surface energy, respectively, for example prior to metallization, printing, or dyeing. Or otherwise, it may be activated to provide favorable conditions for the growth of biological tissues on a polymer material. A polymer surface can be activated by an attachment of various polar functional groups thereto. If passivation of a surface is desired (e.g., reduction of wettability or surface energy, respectively, for example to render textiles hydrophobic or to inhibit the propagation of microorganisms on biocompatible materials), a thin layer of non-polar functional groups may be applied to a surface. The application of functional groups is termed functionalization of a polymer material. Functionalization may be achieved by various treatments, primarily by exposure of a polymer material to a cold plasma. In the case of activation, oxygen or nitrogen containing plasma is often used. In the case of passivation, fluorine and chlorine are chosen. Such treatments enable achieving a wide range of polymer wettability, from moderate hydrophilicity to significant hydrophobicity.
It is sometimes desirable to render one portion of a polymer material hydrophilic and another portion hydrophobic. In such cases, a polymer surface may be partially activated, and partially passivated. This condition is achievable by doping a portion of the polymer material surface during activation or passivation, respectively. In practice, such protection is feasible on relatively large surfaces. If, however, a conversion of functional groups is desired at the microscopic scale, the protection against the action of plasma is a very difficult task.
Functional groups on a polymer surface are not permanent, and their concentration diminishes with time. This phenomenon is termed defunctionalization. The defunctionalization rate is dependent on various factors, such as the type of materials, functional groups, functionalization, and the characteristics of the atmosphere in which the functionalized materials are kept, the optional exposure to light (especially ultraviolet), and various other irradiations. The defunctionalization rate usually increases with increasing temperature.
3. State of the Art
Activation by plasma treatment is oftentimes applied in medicine to activate various artificial implants made of polymeric materials. US2003207099 discloses a two-step method for the treatment of a polymer membrane, resulting in enhanced wettability and permeability of its surface. By a first surface treatment, the membrane surface is activated and becomes very hydrophilic, and a second treatment permanently stabilizes the activation. Similarly, U.S. Pat. No. 5,369,012 discloses the modification of a hydrophobic surface into a hydrophilic surface by exposing the membrane to an oxygen-plasma. WO0204083 discloses a method for the modification of hydrophobic surface properties of a polymer membrane into hydrophilic properties by exposing the membrane to a plasma.
Plasma-assisted surface modification of polymers for medical devices, such as artificial joints, is also used to enhance the surface resistance against detrimental processes, which cause the disintegration of the polymer surface into particles. Such particles may lead to inflammation of the tissues, and pain. US20030040807 discloses a plasma-assisted treatment of medical devices, resulting in the crosslinking of a polymeric material, which becomes more resistant. Simultaneously, the durability of the medical devices and the hydrophilicity of their surface are enhanced, making them more biocompatible. Similarly, WO0134312 discloses a surface treatment of polymeric materials used in medicine. The method comprises a plasma treatment of a material leading to various advantageous effects dependent on the gas, and treatment conditions. Such effects comprise a crosslinking of the polymer, which enhances its resistance, and its surface hydrophilicity or hydrophobicity, respectively.
EP1462183 discloses a method for a surface treatment of substrates, causing a crosslinking of the polymer by plasma treatment, followed by surface activation.
U.S. Pat. No. 5,849,368 discloses a method for hydrophilicization of a hydrophobic surface by dual plasma-treatment. A first treatment is performed in oxygen-plasma, thereby rendering the surface more polar and activated. A second treatment is performed in nitrogen-plasma, to generate amino groups on the surface, thereby enhancing the adhesion of the surface and a smooth layer, which is subsequently applied to the surface, and serves to reduce the friction of the device in the body.
WO02090112 discloses a method of bonding two polymer materials without an adhesive. The surface of one material is activated by a plasma or a laser beam, and placed in contact with an equally activated surface of another material. The joined materials are subjected to high pressure and temperature, thereby bonding the materials.
U.S. Pat. No. 6,479,595 discloses a method of high-pressure plasma treatment of hydrophobic polymer materials in order to render them hydrophilic, for increased dyeability of the surface with water-based dyes. JP8109229 discloses a method of activating the surface of polyvinyl materials for increasing the dyeability of the materials. DE10204472 discloses a method of treating a polymer material surface to be printed, which comprises a first step of making the surface hydrophilic by plasma treatment, and a second step of making the upper layer hydrophobic by laser treatment.
Numerous patents relate to the theme of subjecting non-polymeric materials to a plasma treatment. U.S. Pat. No. 6,187,391 discloses a method for plasma treatment of a textile fabric, which comprises coating a sizing agent inactive to plasma on one surface of the textile, and subjecting the other side to a cold plasma, to form active sites for the polymerization of the monomers. In clothing made of such textiles, sweat can easily be shifted from one surface to another thereof, and can be evaporated.
WO0246282 discloses a method of plasma treatment of porous materials, whereby they become hydrophilic. US20040213918 discloses a method for the functionalization of porous materials. A functionalizing monomer is deposited on their surface by means of vacuum vapor-deposition (VVD). The resulting polymer improves the adherence and durability of metallic and ceramic coatings on the surface of the materials. WO9832789 discloses a method for the functionalization of porous materials throughout the surface, including the surfaces of the pores. Thus, the surface becomes hydrophilic. U.S. Pat. No. 4,694,092 discloses a process for performing plasma treatment on a porous silica gel, whereby its surface becomes hydrophilic, and its pores remain hydrophobic.
U.S. Pat. No. 4,845,132 discloses a method for the modification of a hydrophobic porous membrane by plasma irradiation. Graft chains of a hydrophilic monomer are formed on a surface.
WO9812368 discloses a method for plasma treatment of carbon fibrils or fibril structures, respectively, to modify their surface properties.
U.S. Pat. No. 5,124,173 discloses a method of plasma surface treatment of plastics, by means of argon, helium, and/or ketones. The surface is modified to become hydrophilic, whereby its resistance is enhanced.
CN13027067 discloses a method for the activation of powder particles during the sintering process, resulting in an activation of the produced sintered materials.
U.S. Pat. No. 5,357,005 discloses a method for the activation of dielectric polymers applicable in electronics, by means of a treatment with water vapor plasma. The chemical and physical properties of a surface are modified, whereby its adhesion is enhanced.
U.S. Pat. No. 5,804,263 discloses a method for the treatment of hydrophobic materials having metallic, ceramic, or glass surfaces. The surface is first plasma activated, then exposed to unsaturated monomers, and to gamma-irradiation or electron beam irradiation, which induces polymerization of the monomers and a formation of a hydrophilic coating on the surface. US2002025387 discloses a process for the plasma activation of metallic materials having a web form. US20030168157 discloses a method for the treatment of fluoropolymer tubes to enhance their adhesive properties, wherein plasma activation is used as an intermediate step, prior to applying various polymers to the substrate. The activation is achieved by exposure of the sample to a gas plasma discharge, chemical baths, or an excimer laser, and combinations thereof. Similarly, DE19856227 discloses a method for the plasma activation of fluoropolymers prior to applying a layer of different polymers thereto.
WO03068846 discloses a method for modifying silicone rubber based substrates by plasma treatment. WO02103077 discloses a device for the activation of mobile substrates having a large surface.
All of the above enumerated methods for the modification and functionalization, respectively, of a material suffer from the following disadvantages that restrict their applicability: the modification and functionalization are not localized. The methods described in the above enumerated references do not impart a site-dependent modification to a material. The above art deals with methods for the functionalization by means of chemicals or plasma, whereby the total surface of a material always is modified. Such methods allow localized functionalization only with appropriate doping, which is not easily achieved in practice.